Circularly Polarized Microstrip Antennas with Proximity Coupled Feed for Circularly Polarized Synthetic Aperture Radar

Synthetic aperture radar (SAR) is an active sensor that can produce high resolution imagery in microwave bands. A circularly polarized SAR (CP-SAR) to be launched onboard a micro-satellite is currently developed in the Microwave Remote Sensing Laboratory (MRSL) of the Center for Environmental Remote Sensing (CEReS), Chiba University. As part of the project, an airborne CP-SAR development is also undertaken in order to obtain sufficient knowledge of CP-SAR sensor systems. An L-band CP-SAR system will be designed for operation onboard an unmanned aerial vehicle (UAV). Conventional SAR systems have been based on linearly polarized (LP) antenna systems (Nemoto et al. 1991, Raney et al. 1991). However, there are limitations due to the propagation phenomena. Especially for space propagation, electromagnetic waves propagating through the ionosphere interact with electrons and magnetic fields. As a result, the polarization vector of the electric field is rotated by the Faraday rotation effect (Rignot, 2000). The destructive effects mentioned above of a SAR sensor with linear polarization can be solved by the use of CP-SAR. In addition, it has been pointed out (Raney, 2007) that a full characterization of SAR signals backscattered from a random object can only be possible through the use of circular polarization. Hence, compared to a linear SAR sensor, a greater amount of information about scenes and targets being imaged would be provided with a CP-SAR sensor. The operational frequency is chosen to be 1.27 GHz in L-band considering its superior features on particular applications. As the Microwave Remote Sensing Laboratory, Center for Environmental Technology, Chiba University is developing a CP-SAR sensor onboard an UAV, an antenna for the Lband CP-SAR sensor is required.